Tagged Questions

A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

As the particles which constitute a black hole collapse they become tightly bound. I assume this means a lot of energy would be required to liberate a particle from that bound state. Is it a finite ...

We've heard it many times, nothing can escape the gravity of a black hole, even light once it's past the event horizon. If this is true, how can a black hole emit anything? Quasars are massive black ...

If the gravitational pull of a black hole is strong enough to stop the speed of light from leaving it , then wouldn't a quasar have to travel faster than the speed of light, at some point, to break ...

I understand that accretion of normal matter into a super-massive black hole leads to x-ray emissions. Is the same effect expected to occur for dark matter accretion into a supermassive black hole? ...

If you were to fly around a black hole, would the gravitational pull be uniform and centered on the singularity, regardless of your relative location?
If yes, how can this be consistent with models ...

Do free massless particles have a Schwarzschild radius? I'm curious about the mass in the equation for the Schwarzschild radius. I know that you can calculate a Schwarzschild radius for any massive ...

If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a ...

It just vanishes into space leaving nothing behind or does it expel some material?
Also, talking more about black holes, as far as i understand the term "temperature", it is defined by the amount of ...

I'm having trouble differentiating the following when making a change of co-ordinates to determine the Schwarzschild metric.
$$r'^{2}=r^{2}C(r)$$
Then taking the total derivative of both sides, the ...

We have images of stars orbiting black holes or black holes destroying near stars, but why do we see the stars moving normally? I mean, if time dilation does exist, shouldn't we see that stars slow ...

Assume two black holes in the most common size range, spiraling into each other until they merge. The event releases significant amounts of energy via gravitational waves, which warp the space-time.
...

If a matter condensed into small enough (schwarzchild radius) we can create Blackholes. I have trouble understanding this concept. Does the black hole created for example by compressing a tennis ball ...

Assumption that wormholes really exist. Even if humanity could produce wormholes from quantum black holes. These would be never traversable due to the effect of spaghettification?
Or does the exotic ...

The following formula has been given in 't Hooft's black holes notes ($|\Omega \rangle$ is the vacuum state of Minkowski space, O is a operator):
$$\langle \Omega| O|\Omega \rangle = \sum_{n \ge 0} ...

I am not talking about event horizons. I am talking about the actual remnant of stellar collapse.
Is it just a point, hence the problem with the singularity? Or does it have a finite volume that we ...

As you come in closer to a black hole, how do you see the event horizon? Is it always like a clear-cut surface? Or it only looks clear-cut from a distance, but as you come closer to the black hole, ...

How is it possible for an object like a black hole or electron to spin since they are made up of no other components? If my understanding is correct, an electron is an elementary particle which means ...

I know there are many ways in detecting a black hole, but there are odds against them too. So I wanted to know a accurate method to detect a black hole.
Here are the known methods to me and the odds ...

In the context of energy extraction of spinning black holes, there are two known mechanisms: the Penrose process and the Blandford-Znajek process. The former relies on fragmentation of accreting flow, ...

Bekenstein and Hawking derived the expression for black hole entropy as,
$$
S_{BH}={c^3 A\over 4 G \hbar}.
$$
We know from the hindsight that entropy has statistical interpretation. It is a measure ...

This question came to my mind when i saw the movie interstellar.
In the movie there is a scene with a black hole and a sphere of light around it, what i assume to be the photon sphere.
You can see it ...

I understand that, to break the entanglement of two particles of Hawking radiation and therefore preserve monogamy of entanglement, there should be a firewall around the event horizon. This firewall ...

I came across this term and I heard they used sonic black holes to detect something analogous to hawking radiation, but I have failed to find sources which explain how exactly they work and how they ...

The temperature of Hawking radiation is inversely proportional to the mass of a black hole, $T_{\rm H}\propto M_{\rm BH}^{-1}$, and so as the black hole shrinks the temperature of the radiation should ...